The Middle History
The M4A1 and the F88SA1/2
From about 1990, Colt designed a shorter version of the M16, called the M4. In 1993, the US military adopted the M4 as a personal defence weapon for people like armoured crewman and logisticians and a modular short barrelled rifle for Special Forces (the M4A1, which came with a generous and very modern accessory kit with sights, silencers, grips and so on called the SOPMOD kit[i]). The M4 was 29.5-33 inches long, had a 14.5 inch barrel and weighed about 2.9kg. It is notable for introducing the first modular and universal mounting system for accessories (including optics) called the MIL-STD 1913 'Picatinny' rail system[ii], for being very light, and for including an adjustable stock that allows users of different sizes to modify its length of pull for optimal hold and sight pictures with and without body armour. Prior to the introduction of MIL-STD 1913, a variety of non-standard mounting systems, including duct tape, were used for accessories[iii]. In 1998, 1 Sqn SASR were exposed to the SOPMOD M4A1 on deployment in Kuwait. They had never been fans of the F88 due to problems the rifle initially had with quality control and amphibious operations and they now had a system that was (on paper at least) purpose built to be a modular special forces rifle[iv]. SASR adopted the M4A1-AUS in 1999.
When first used for serious fighting from 2001 in the Global War on Terror (GWOT), the M4A1 (which was really originally a purpose-built personal defence carbine; to be carried always and fired sometimes[v]) was pushed past its design limits and had substantial problems. In firefights receivers cracked, barrels exploded, bolts broke, enemy combatants required multiple hits to be incapacitated, and the weapon suffered from very high stoppage rates[vi]. From about 2002 onwards, design improvements to the M4A1 occurred that improved nearly all these issues. By 2011, 63 improvements had been made with a program of improvements continuing after that date[vii]. US Special Forces started a program to replace their M4A1 rifles with more reliable and lethal rifles (the SCAR program which birthed the HK416, FN-SCAR and so on[viii])[ix]. While questions about reliability lingered[x], the M4 was undoubtedly lighter and handier than the M16 and it was evidently considered reliable enough to become the service rifle of the US Army by 2006[xi]. Despite popularity with many marines, the USMC would never really institutionally accept the M4 as a service rifle, officially adopting it briefly from 2015[xii], prior to replacing it with the M27 in 2018[xiii].
Wikimedia Commons / Offspring 18 87
The lethality problems were harder to solve. The heavier M855 armour piercing[xiv] ammunition that the US had adopted with the M16A2 can exhibit poor wounding characteristics at even fairly close ranges when fired from the short barrel of an M4. These problems were also experienced by Australian Special Forces, for example one SASR Major commented in a 2009 post operation debrief that 'I shouldn’t have to hit a bloke five times before he stops.'[xv]. US Special Forces started using much heavier open tip match ammunition originally intended for designated marksmen (the MK262) which coincidentally has desirable terminal ballistics[xvi]. However, that ammunition has no ability to penetrate body armour and so is unsuitable for use in conventional warfare against enemy combatants who will almost certainly wear body armour and helmets[xvii].
The US Army eventually adopted an armour piercing round with very high velocity even from short barrels (the M855A1)[xviii], but the very high chamber pressure needed to get the required muzzle velocity tends to destroy rifles from which it is fired[xix]. There was substantial speculation in this the period that the US would have to adopt a bigger round to solve the problem (6.8x43mm SPC was widely touted on the internet as a likely successor) but this hasn’t yet occurred and it is not clear whether it ever will (although the US Army Next Generation Squad Weapons project continues to operate with a goal of first issuing 6.8mm individual weapons in 2021[xx]).
The rail system on the M4 was a world leading concept, rapidly becoming the industry standard, and the Australian Defence Force upgraded the F88 to include such rails with the F88SA1 in 1999[xxi]. Unfortunately, the way that this was achieved increased the weight of the rifle, by a lot, to 4.3kg unloaded without other substantial changes to the overall design of the weapon. When the rifle was upgraded to the F88SA2 in 2009, the weight increased again to 4.4kg unloaded and aside from slightly improved mounting options (an extended top rail to improve sight pictures using Trijicon ACOGs and better options for mounting illumination devices) there were only minor changes to the design. The author was not able to find evidence that these weight gains were considered to be a problem by the capability manager (Army) and are understood to have been considered to be acceptable tradeoffs for the improved mounting options of the two rifles[xxii]. This is the period when many Australian soldiers began complaining about the F88 and arguing that it should be replaced with an M4-based rifle.